Self-closing flushing valves for the purposes above described are known. For example, in Israel Patent No. 60774 there has been disclosed a flushing valve based on the coaction between a pair of membranes, one controlling the outlet of a flush water discharge outlet, and the other responsive for closing the first membrane after a certain pressure has been built-up between the membranes.
This type of flushing valves suffers from numerous disadvantages, mainly and in that its operation is based on a pressure equilibrium condition, which is difficult to preset and is liable to be effected by different operating conditions of the line, e.g. pressure, amount of flow, etc. Furthermore, the structure is based on an in-line emitter unit installed therein, and generally comprises a relatively large number of components some of which are of non-standard design and therefore is rather costly in production.
It has also been proposed to provide flushing valves such as disclosed in U.S. Pat. No. 4,022,244, which are based on the principle of pressure triggering operation, namely such that it enters into operation upon a certain, nominal pressure prevailing in the line, and shuts-off when the pressure drops below the operative level. The operation of these valves is of course conditional upon reaching the predetermined operating pressure, which, in turn, cannot be completely guaranteed under normal, field working conditions.
It is thus the general object of the present invention to provide a flushing valve of the above type that will overcome the disadvantages of the prior art valves.
It is a further object of the invention to provide a flushing valve, the operation thereof being independent of the availability of initial and/or ultimate pressure conditions.
It is a still further object of the present invention to provided a flushing valve of a simple, straightforward structure with minimum number of components.
It is a still further object of the present invention to provided a flushing valve suitable for lines of standard, stick-in drip-irrigation emitter units.